The present embodiments relate to wireless communications systems and, more particularly, to communication of primary and secondary synchronization codes in such systems.
Wireless communications have become very prevalent in business, personal, and other applications, and as a result the technology for such communications continues to advance in various areas. One such advancement includes the use of spread spectrum communications, including that of code division multiple access (“CDMA”) and wideband code division multiple access (“WCDMA”) cellular communications. In such communications, a user station (e.g., a hand held cellular phone) communicates with a base station, where typically the base station corresponds to a “cell.” To accomplish the communication from a user station to a base station, the user station must synchronize itself to a base station, and this synchronization process requires the user station to detect both a primary synchronization code (“PSC”) and a secondary synchronization code (“SSC”) as transmitted from a base station. The PSC is transmitted with the same encoded information for numerous base stations while each base station transmits a unique SSC. The synchronization process typically occurs when a user station is initially turned on and also thereafter when the user station, if mobile, moves from one cell to another, where this movement and the accompanying signal transitions are referred to in the art as soft handoff. Once the PSC is detected, the user station is thereby informed of the periodic timing of the communications. Once the SSC is detected, the user station is thereby informed of the data (i.e., frame) location within the base station communications. Further, once the user station has detected a unique base station SSC, the user station also may identify a so-called group of long codes that is also unique to, and transmitted by, the base station, where that long code is then usable by the user station to demodulate data received from the base station.
While various approaches have in the past been proposed or implemented in connection with the synchronization methods described above, the present inventors have determined that such approaches may be improved. For example and as detailed later, when a user station attempts to identify the SSC of a base station, the user station typically implements a correlation evaluation technique to decipher transmissions from the base station, where an example of such a technique is a Walsh-Hadamard transform. The technique effectively allows the user station to compare different possible SSCs with the actual SSC embedded in the base station's transmissions. When a sufficiently large correlation is detected, then the user station has a corresponding level of confidence that it has detected the base station's SSC. While the preceding approach provides a certain probability that an SSC will be detected properly by a user station, it is recognized in connection with the present inventive embodiments that such a probability may be improved as compared to the prior art. Specifically, it is further recognized in connection with the present inventive embodiments that a prior art approach may provide false SSC detections by the user station, that is, a user station may conclude that it has detected a base station SSC due to a high cross-correlation finding during the user station's analysis, when in fact the high cross-correlation arises from a different SSC that does not correspond to the actually correct base station SSC. In this case, if the user station concludes it has detected the proper SSC when in fact it has detected an erroneous SSC, then the user station may attempt to communicate with the base station while using an incorrect SSC and thereby preventing such communications from properly occurring. Thus, as the user station compares various possible SSCs against a base station transmission having a unique base station SSC, there is a need to present a relatively large correlation detected by the user station when the proper SSC is being considered as compared to presenting a relatively small correlation detected by a user station when other SSCs are being considered. This need is addressed by the preferred embodiments, as described below.